Deflection of mantle flow beneath subducting slabs and the origin of subslab anisotropy

Abstract Global compilations of subslab shear wave splitting parameters show a mix of trench-parallel and trench-perpendicular fast directions that often directly contradict predictions from two-dimensional models of slab-entrained flow. Here we show that subslab anisotropy is consistent with three-dimensional geodynamic models that feature the interaction between subducting slabs and regional mantle flow. Each model represents a specific region for which high-quality source-side shear wave splitting data are available. We compare the distribution of finite strain in the models with shear wave splitting observations, showing that both trench-parallel and trench-perpendicular fast directions can be explained by deflection of regional mantle flow around or beneath subducted slabs. Subslab maximum elongation directions calculated from our models depend on a combination of geometry factors (such as slab dip angle and maximum depth), mechanical parameters (such as decoupling between the slab and the subjacent mantle), and the orientation and magnitude of the regional mantle flow

A Late Cretaceous true polar wander oscillation

True polar wander (TPW), or planetary reorientation, is well documented for other planets and moons and for Earth at present day with satellites, but testing its prevalence in Earth’s past is complicated by simultaneous motions due to plate tectonics. Debate has surrounded the existence of Late Cretaceous TPW ca. 84 million years ago (Ma). Classic palaeomagnetic data from the Scaglia Rossa limestone of Italy are the primary argument against the existence of ca. 84 Ma TPW. Here we present a new high-resolution palaeomagnetic record from two overlapping stratigraphic sections in Italy that provides evidence for a ~12° TPW oscillation from 86 to 78 Ma. This observation represents the most recent large-scale TPW documented and challenges the notion that the spin axis has been largely stable over the past 100 million years

Re-visiting Meltsner: Policy Advice Systems and the Multi-Dimensional Nature of Professional Policy Analysis

10.2139/ssrn.15462511-2

Characterization of a nucleoside/proton symporter in procyclic Trypanosoma brucei brucei

Adenosine transport at 22 degrees C in procyclic forms of Trypanosoma brucei brucei was investigated using an oil-inhibitor stop procedure for determining initial rates of adenosine uptake in suspended cells. Adenosine influx was mediated by a single high affinity transporter (K-m 0.26 +/- 0.02 mu M, V-max 0.63 +/- 0.18 pmol/10(7) cells s(-1)). Purine nucleosides, with the exception of tubercidin (7-deazaadenosine), and dipyridamole inhibited adenosine influx (K-i 0.18-5.2 mu M). Purine nucleobases and pyrimidine nucleosides and nucleobases had no effect on adenosine transport. This specificity of the transporter appears to be similar to the previously described P1 adenosine transporter in bloodstream forms of trypanosomes. Uptake of adenosine was Na+-independent, but ionophores reducing the membrane potential and/or the transmembrane proton gradient (monitored with the fluorescent probes bis-(1,3-diethylthiobarbituric acid)-trimethine oxonol and 2',7'-bis(carboxyethyl)-5,6-carboxyfluorescein acetoxymethyl ester, respectively) inhibited adenosine transport. Similarly, an increase in extracellular pH from 7.3 to 8.0 reduced adenosine influx by 30%. A linear correlation was demonstrated between the rate of adenosine transport and the protonmotive force. Adenosine uptake was accompanied by a proton influx in base-loaded cells and was also shown to be electrogenic. These combined results indicate that transport of adenosine in T. brucei brucei procyclics is protonmotive force-driven and strongly suggest that the adenosine transporter functions as an HC symporter